Examples of the conventional rotational force transmitting apparatuses include a rotational force transmitting apparatus in which rotation of an input-side gear is transmitted to an output-side gear via multi-stages of gears and a rotational force transmitting apparatus in which a rotation shaft of a motor or a rotation shaft of another gear is connected to an output shaft via a rotation transmitting member such as a key and a spline.
However, those conventional rotational force transmitting apparatuses have jolting (a slightly moving state, not fixed completely as a machine) caused by backlash between gears, a slight gap between a key and an output shaft, or the like. The conventional rotational force transmitting apparatuses further have a structure in which jolting in a rotational direction is accumulated before a rotational force is transmitted to the output shaft. In such a structure, in a stationary state in which a rotational force is not inputted to an input side, jolting accumulated in the rotational direction as described above is caused in the output shaft.
In view of this, there is proposed a mechanism for reducing jolting of an output shaft. This mechanism is a combination of a rotational force transmitting mechanism including a plurality of gears and a reverse input clutch. The reverse input clutch transmits an input-side rotational force to the output shaft, but does not cause the output shaft to rotate due to a rotational force inputted from an output side.
For example, in an invention described in Patent Document 1, a motor, a speed reducer for reducing a speed of torque inputted from the motor, and a reverse input prevention clutch for inputting the torque from the speed reducer to an input-side member and outputting the torque from an output-side member are integrated as a unit.
According to this conventional art, the output-side member has a structure in which even if jolting in a rotational direction is accumulated in the output-side member by the motor, the speed reducer, or the like, the output-side member is not rotated by a rotational force from an outside. Therefore, in a stationary state in which a rotational force is not inputted to an input side, it is possible to prevent jolting of an output shaft in a circumferential direction. However, in order to apply this conventional art, in particular, to a thin and small actuator, a further devise is necessary, and improvement in productivity thereof is also demanded.